Rotational Inerter Flywheel for Aircraft Actuator Flutter Damping
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Solution Overview
Problem
Aircraft actuators face challenges in preventing control surface flutter due to overlapping operating bandwidth and resonant frequency, leading to increased oscillations and potential structural failure, which is exacerbated by the size and weight of hydraulic systems required to mitigate this issue.
Innovation Solution
The implementation of a rotational inerter that couples a flywheel to the actuator's rod and threaded shaft, allowing axial acceleration to induce proportional rotational acceleration, thereby reducing oscillatory amplitudes and enabling the actuator's operating bandwidth to match or encompass the resonant frequency without increasing inertia or size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the operating bandwidth of the flight control system overlaps the resonant frequency of the flight control surface, then the actuator can respond to control commands across a wider range of frequencies, but control surface flutter occurs leading to unstable oscillations and potential structural failure
Solution Approach 1:
The patent introduces a flywheel as an intermediary inertial element coupled between the actuator and the flight control surface. The flywheel acts as a mediator that absorbs and dampens oscillatory forces, allowing the system to operate at resonant frequencies without transmitting destabilizing vibrations to the control surface, thus resolving the contradiction between bandwidth and stability
Solution Approach 2:
The patent modifies the inertial parameters of the actuator system by adding a flywheel with specific moment of inertia. This parameter change transforms the system's dynamic response characteristics, enabling it to pass through resonant frequencies safely by altering the mass distribution and inertial properties of the actuation mechanism
2Reliability
If the inertia of the load on the actuator is limited to avoid resonance, then control surface flutter is prevented, but the control surface area must be decreased reducing attitude controllability
Solution Approach 1:
The patent segments the inertial mass into two distinct components: the lightweight flight control surface and the separate flywheel. This segmentation allows the control surface to maintain its full area for effective control authority while the flywheel provides the necessary inertial damping to prevent resonance, resolving the contradiction between reliability and surface area
3Reliability
If the piston cross-sectional area of the actuator is increased to react larger inertia loads, then the actuator can handle higher inertia without resonance, but the size and weight of the hydraulic system increases resulting in increased aerodynamic drag
Solution Approach 1:
The patent uses the flywheel as a counterweight that provides inertial reaction forces to balance and dampen oscillatory loads. This allows the actuator to handle high inertia loads without requiring an oversized piston, thereby avoiding the need for increased hydraulic system weight and volume while maintaining reliability
Solution Approach 2:
The patent transitions from a static, oversized actuator design to a dynamic system where the flywheel's rotational inertia actively responds to oscillatory conditions. The flywheel's moment of inertia is specifically tuned to provide damping at resonant frequencies, allowing a smaller, lighter actuator to perform the same function without compromising reliability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces actuator load oscillatory amplitude by up to 10% at resonance, allowing for a smaller, lighter actuator system that maintains stability and reduces aerodynamic drag, enhancing aircraft performance and efficiency.
Implementation Method 1
a flywheel having a flywheel annulus coupled to the rod. The flywheel is configured to rotate in proportion to axial acceleration of the rod relative to the threaded shaft
Implementation Method 2
a threaded shaft coupled to and movable with the second terminal. The flywheel is rotatably coupled to the rod and threadably engaged to the threaded shaft
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An apparatus for damping an actuator (202) includes an inerter (300). The inerter (300) includes a first terminal (302) and a second terminal (304) movable relative to one another along an inerter axis (306) and configured to be mutually exclusively coupled to a support structure (116) and a movable device (124) actuated by an actuator (202). The inerter (300) further includes a rod (224, 308) coupled to and movable with the first terminal (302) and a threaded shaft (322) coupled to and movable with the second terminal (304). The inerter (300) further includes a flywheel (314) having a flywheel annulus (318) coupled to one of the rod (224, 308) and the threaded shaft (322). The flywheel (314) is configured to rotate in proportion to axial acceleration of the rod (224, 308) relative to the threaded shaft (322) in correspondence with actuation of the movable device (124) by the actuator (202).